Romans 3:15

"What then have we more than they? For we have proved both Jews and Gentiles, that they are all under sin. As it is written, There is none righteous, no, not one." He had accused the Gentiles, he had accused the Jews; it came next in order to mention the righteousness which is by faith. For if the law of nature availed not, and the written Law was of no advantage, but both weighed down those that used them not aright, and made it plain that they were worthy of greater punishment, then after this the salvation which is by grace was necessary. Speak then of it, O Paul, and display it. But as yet he does not venture, as having an eye to the violence of the Jews, and so turns afresh to his accusation of them; and first he brings in as accuser, David speaking of the same things at length, which Isaiah mentioned all in short compass, so furnishing a strong curb for them, so that they might not bound off, nor any of his hearers, while the matters of faith were laid open to them, might after this start away; being beforehand safely held down by the accusations of the prophets. For there are three excesses which the prophet lays down; he says that all of them together did evil, and that they did not do good indifferently with evil, but that they followed after wickedness alone, and followed it also with all earnestness. And next that they should not say, "What then, if these things were said to others?" he goes on:

Scripture says this about the murder of the prophets, whom they killed without hesitation—"slow to do good but swift to murder."

Destruction and misery are in their ways, and the way of peace have they not known. The fear of God is not before their eyes.

Then when he says their feet swift he touches on sinful deeds, in regard to which he mentions three things. First, readiness to do wickedly. Hence he says, their feet swift, i.e., their feelings, to shed blood, i.e., to commit any serious sin, because among …

Their feet are swift to shed blood. The sins of the heart and mouth are before described, and now the sins of action are taken notice of; for "the feet" are the instruments of motion and action: and when these are said to be "swift to shed blood", it denotes the readiness and eagerness of men, to murder innocent creatures; which shows the dreadful malice and hatred that is in them.